The following abbreviations are herewith defined, at least some of which are referred to within the following description of the state-of-the-art and the present invention.    GPON gigabit (enabled) PON    I2C inter-integrated circuit    LBC laser bias current    LED light emitting diode    MDU multi-dwelling unit    MPC monitor photodiode current    OLT optical line termination    ONT optical network termination    PON passive optical network
An increasing number of communications systems use optical transmission for carrying signals to transmit information. Optical networks may be used for both voice and data transmission, such as telephone service and Internet access, as well as for the transmission of television programs and other media. Optical networks use light produced by lasers or LEDs that is transmitted along fiber optic cables. Optical networks are high capacity and preferred in many applications. Although bundled fiber optic cables have for some time been used for high-capacity, long-distance transmissions, fiber to the home and fiber to the curb implementations are becoming more common as the infrastructure is built out.
A widely-used type of optical network is a PON. Herein, this term is meant to include the various evolutions of the PON, such as a GPON. In an exemplary PON, an OLT is connected by fiber optic cable to a number of ONTs. An OLT is frequently located in the network provider's switching office and may serve several dozen separate ONTs. The OLT receives information from content and service providers for transmission to the subscribers through their respective ONTs. Although in most cases this downstream traffic accounts for the majority of system transmission, each ONT also transmits information upstream to the OLT, which then can process and forward it on to its intended destination.
Note that as used herein, “ONT” is intended to refer broadly to all subscriber-based optical network components. Different ONTs may, for example, be associated with a particular residence, while others may be associated with apartment buildings and small businesses, and permit access for a number of separate subscribers. ONTs are typically demarcation points, terminating the provider's optical network at a subscriber's premises. From these ONTs, a connection is made to the subscriber's equipment, in many cases through a home network to which multiple devices have access.
Because there is more downstream transmission bandwidth available, each ONT is assigned time slots for upstream transmission, during which buffered information, if any, is sent as a burst during an available slot. Scheduling is normally done by the OLT. Time slots are tightly scheduled, however, to maximize the available transmission time. Precise calculations are made to ensure that each ONT transmits at the right time, including a process called ranging. In ranging, the PON goes through a procedure so that the OLT may discover each ONT to which it is actively connected, and gauge the physical distance separating it from the OLT. A delay associated with that distance is used to adjust the time slot for the respective ONT. As should be apparent, this timing is very important and ONTs that transmit at the wrong time may disrupt communications for the entire PON.
One problem encountered in this carefully-executed scenario is the rogue ONT. A rogue ONT is one that is currently over-transmitting, and therefore transmitting, at least part of the time, at the wrong times. This may occur, for example, because the optical transmitter in the ONT is stuck in an ‘on’ configuration, although a rogue ONT is not necessarily ‘on’ all of the time.
Although the remedy for a rogue ONT situation will often be to simply shut down the offending components, temporarily or until a repair or restart may be affected, there are often practical obstacles to doing so. First, the offending ONT must somehow be detected. The OLT will naturally be able to perceive in most cases that transmissions on the PON are not occurring normally. But since in this event a rogue ONT is likely transmitting at the wrong time, or disrupting the transmissions from the ONTs to the OLT, it may be difficult to identify the offending ONT. Therefore existing solutions that rely on communication between the OLT and one or more ONTs are often not satisfactory.
One possible scheme is to monitor the burst enable signal (related to the ONT' s allocated timeslot) for an optical laser or other light source, but failures beyond this control point may leave the ONT open to additional faults that are not detectable in this manner. The monitoring of LBC is another possibility, but due to the burst nature of PON transmissions, the measurements taken in this case are in and of themselves less than satisfactory for detecting a rogue ONT.
Note that the techniques or schemes described herein as existing or possible are presented as background for the present invention, but no admission is made thereby that these techniques and schemes were heretofore commercialized or known to others besides the inventors.
Accordingly, there has been and still is a need to address the aforementioned shortcomings and other shortcomings associated with regulating rogue ONTs and other, similar, optical transmission components. These needs and other needs are satisfied by the present invention.